Downloaded from http://mem.lyellcollection.org/ by guest on October 2, 2021 Editorial to the revised reprint This edition of the atlas is a reduced-size reprint of the original A3 atlas. the Ar-Ar method and those obtained from Pb/U, Rb/Sr and K/Ar methods That work, the most expensive publishing venture hitherto undertaken by (Menning et al. 1997). The suggested compromise dates for the maps are: C1 the Society, has covered its costs, so the opportunity exists to produce this 354 Ma, C2 348 Ma, C3 343 Ma, C4 337 Ma, C5 325 Ma, C6 315 Ma, C7 smaller sized version at a low cost. 312 Ma, C8 309 Ma, C9 304 Ma. Inevitably in the time that has elapsed since the atlas was produced there The identification of early Dinantian evaporites in the Solway Basin have been some major publications that have impinged upon the map extending over more than 1000 km 2 implies arid and semi-arid conditions reconstructions. The decision was made, to enable the price to be kept as across that basin around Chadian and Arundian ages (Ward 1998). Cyclic low as possible, that no amendments would be made to the maps or text for successions were correlated with glacio-eustatic sea-level oscillations and the this edition, but that this editorial page could be used to draw the readers' identification of this facies requires evaporite symbols over the Solway attention to points where revision is needed. It is not possible in the limited Basin on maps C3 and C4. space available to mention the large number of minor modifications needed to the maps, but an attempt has been made here to summarize some of the Permian and Triassic. No changes are proposed for the maps of these more significant changes required. periods. Edwards et al. (1997) recognized that the Crediton Trough of central Devon is an E-W basin that has a fill of Late Carboniferous-Early Terranes. Controversy still exists about some of the terrane boundaries Permian sediments that is overlain unconformably by a Late Permian shown on the map, but the hypothesis of Terrane Tectonics has gained wide sequence, the two successions being separated by a hiatus of at least 20 acceptance. Unresolved problems include the status of the Grampian Group million years duration. - was it, as the map suggests, the basal part of the Dalradian Supergroup (in which case the Great Glen Fault is a terrane boundary) or was it the Jurassic. For the Jurassic, the late Toarcian uplift has been now firmly uppermost group of the Moine Supergroup (in which case the Great Glen associated with thermal doming of the North Sea centred on the Rattray Fault is simply a post-Moine fault)? At the southern end of the Dalradian volcanic centre. The effects of this thermal doming have been discussed in outcrop similar problems concern the fossiliferous rocks that crop out along detail by Underhill & Partington (1993); they show that the area affected the Highland Boundary Fault zone across the Scottish Highlands and was greater than 1250 km in diameter and have charted the history of the westwards to western Ireland. These fossiliferous units may be part of a doming and the subsequent deflation that persisted through to the late largely hidden terrane (the Highland Border Subterrane as depicted on the Oxfordian. This work allows better palaeogeographical restraint on the map), whilst others argue that they are the youngest component of the maps for the Aalenian-Oxfordian interval and also suggests that there was a Dalradian Supergroup. For a detailed account of the Scottish Precambrian marine connection from the Hebrides through to the Moray Firth across the rocks, the reader is referred to the revised Precambrian correlation charts Great Glen in Bathonian-Oxfordian times (Underhill & Partington 1993, (Gibbons & Harris 1994). fig. 4). Precambrian. New dates for the Torridonian (Turnbull et al. 1996) suggest a Cretaceous. In the Upper Cretaceous the palaeogeographies represented by Stoer Group age of 11994-70 Ma (P~la) and 977+39 Ma for the maps K4a and K4b may now be considered as somewhat conservative Applecross Formation (PC Ib). New dates for the Precambrian-Cambrian reconstructions. The identification of doming centred on the Irish Sea (Cope boundary (Bowring et al. 1993; Landing et al. 1998) suggest that map PC3a 1994) initially suggested from inversion indicated by Apatite Fission Track should be around 565 Ma and PC3b around 545 Ma. Analysis (Lewis et al. 1992, Holliday 1993) strongly suggests that there was a considerable Chalk thickness not only over the Irish Sea, but right over Cambrian. New dates for the Cambrian (Bowring et al. 1993; Davidek et al. mainland Wales (at least by the Campanian, if not much earlier). The 1998; Landing et al. 1998) require revisions to the dates of the Cambrian amount of land shown over the Lake District and the Southern Uplands maps. Revised suggested dates are: Cla 520 Ma, Clb 510 Ma, g2a 498 Ma, may also be too great. Cope (1998) has reconstructed a likely Jurassic and ~2b 520 Ma. Cretaceous cover for the Irish Sea area and its environs. Ordovician. Revisions of the British Ordovician series (Fortey et al. 1995) Palaeogene. The doming of the Irish Sea, referred to under 'Cretaceous' propose that the Llandeilo Series be largely subsumed within an enlarged above probably took place in the earliest Palaeocene and map Pgl should be Llanvirn Series and relegated to stage-level, with the gracilis Biozone modified to show an Irish Sea centred uplift of some 2-2.5 km whose effects marking the base of a revised Caradoc Series. New dates for the Ordovician reached at least as far south as the Chiltern Hills and are responsible for the (Tucker & McKerrow 1995; Davidek et al. 1998) also require changes as 2 ~ regional south-easterly dip of the Anglo-Welsh area (Cope 1994). follows: Ola 487 Ma, Olb 478 Ma (now = earliest Whiterock), O2a 466 Ma, O2b 458 Ma, O3a 454 Ma, O3b 446 Ma, O4a 487 Ma, O4b 480 Ma, O5a Neogene and Quaternary. No changes are proposed for these maps. 466 Ma, O5b 458 Ma (under the new scheme for the British Ordovician series, this would now be earliest Caradoc), O6a 456 Ma, O6b 455 Ma, O7a References 454 Ma, O7b 451 Ma, O8a 446 Ma, O8b 444 Ma. BOWRING, S. A., GROTZINGER, J. P., ISACHSEN, C. E., KNOLL, A. H., PELECHATY, S. M. & KOLOSOV, P. 1993. Calibrating rates of Early Silurian. New dates for the Silurian (Tucker & McKerrow 1995) suggest the Cambrian evolution. Science, 261, 1293 1298. following revised dates for the Silurian maps: Sla 443 Ma, Slb 434 Ma, S2a BOILER, A. J., WOODCOCK, N. H. & STEWARX, D. M. 1997. The Woolhope 433 Ma, S2b 431 Ma, S3a 427 Ma, S3b 424 Ma, S4a 423 Ma, S4b 422 Ma, and Usk Basins: Silurian rift basins revealed by subsurface mapping of S5a 421 Ma, S5b 420 Ma, S6a 443 Ma, S6b 434 Ma, $7 431 Ma, S8a 427 the southern Welsh Borderland. Journal of the Geological Society, Ma, S8b 419 Ma, $9 418 Ma. London, 154, 209-223. COOPER, A. M., MILLWARD,D., JOHNSON, E. W. • SOPER, N. J. 1993. The The record of rapid Rhuddanian and Aeronian subsidence in the early Palaeozoic evolution of northwest England. Geological Magazine, Woolhope and Usk basins recorded by Butler et al. (1997) requires 130, 711-724. modification to the first Silurian map (Sla). These basins, that developed COPE, J. C. W. 1994. A latest Cretaceous hotspot and the south-easterly tilt during rifting of the western part of the Midland Platform, were bordered of Britain. Journal of the Geological Society, London, 151, 905-908. north-westwards by the Neath Disturbance and eastwards by the Malvern -- 1998. The Mesozoic and Tertiary history of the Irish Sea. In: line. Huntley Quarry (indicated on the map) lies at the eastern boundary of MEADOWS, N. S., TRUEBLOOD, S., HARDMAN, N. & COWAN, G. (eds). this area where thinner marginal successions accumulated. The southern The Petroleum Geology of the Irish Sea and adjacent areas. Geological margin of this depositional area (as for map Slb) is conjectural. Society, London, Special Publications, 124, 48-59. [dated 1997] For northern parts of southern Britain, it is now clear that Eastern DAVIDEK, K., LANDING, E., BOWRING, S. A., WESTROP, S. R., RUSHTON, Avalonia was closer to Laurentia by the late Ordovician than was envisaged A. W. A. FORTEY, R. A. & ADRAIN,J. 1998. New uppermost Cambrian when the Atlas was drawn up and that its initial docking against the U-Pb dates from Avalonian Wales and the age of the Cambrian- Laurentian margin took place earlier in the Silurian. It was completed in Ordovician boundary. Geological Magazine, 135, 303-309. early Devonian times, with a component of anticlockwise rotation (Soper & EDWARDS, A., WARRINGTON,G., SCRIVENER, R. C., JONES, N. S., HASLAM, Woodcock 1990). By mid-Ludlow times a migrating foreland basin was H. W. & AULT, A. 1997. The Exeter Group, south Devon, England: a established over the Lake District that accumulated some 7 km of turbidites, contribution to the early post-Variscan stratigraphy of northwest probably largely derived from a Southern Uplands source, but with input Europe. Geological Magazine, 134, 177-197. from Scandia too (Cooper et al. 1993) (requiring amendments to maps S5a FORTEY, R. A., HARPER, D. A. T., INGHAM,J. K., OWEN, A. W. & RUSHTON, and S5b). By the start of Pfidoli times this basin was largely filled and was A. W. A. 1995. A revision of Ordovician series and stages from the subtidal (map S8b). historical type area. Geological Magazine, 132, 15-30.